Skin Part One

Learning Objectives

• Key Functions of Skin: Understand the multiple roles skin plays in animal physiology.

• Temperature Regulation: Discuss mechanisms of thermoregulation in domestic animals.

• Thermo-Neutral Zone: Comprehend the thermal neutrality zone and its effect on animal welfare and production.

• Vitamin D Formation: Outline how vitamin D is synthesized in the skin and identify species prone to deficiency.

Functions of the Skin

A. Epidermis

• Provides waterproofing and mechanical protection.

B. Dermis

• Contains fur follicles along with muscles, veins, arteries, and thermoreceptors.

C. Subcutis/Hypodermis

• Functions in insulation and as an energy store; composed of adipose cells.

D. Adipose Cells

• Assist in heat retention and act as energy reserves.

E. Pili Erector Muscle

• Adjusts hair position for temperature regulation by trapping air for insulation or releasing heat.

Temperature Regulation in the Skin

• Core Temperature: Remains stable within 1 degree Celsius, while skin temperature can vary by up to 20 degrees depending on the environment.

• Physiological Mechanism: Involves feedback from receptors in the skin to the hypothalamus that controls thermoregulation.

Physiological and Behavioral Responses to Heat

Internal Mechanisms

• Mechanisms include changes in blood flow and heart rate to regulate temperature.

Behavioral Responses

• Examples: Seeking shaded areas, panting, reducing locomotor activity, licking skin for evaporative cooling.

Physiological Mechanisms in Various Breeds

• Chinese Crested Dog: Engages in behavioral modifications to cope with heat.

• Sphynx Cat: Displays unique adaptations to thermoregulate effectively.

• Xoloitzcuintli Dog: Similar physiological adaptations to cope with heat.

Shivering and Temperature Responses

Mechanisms of Shivering

• Involves pre-motor neurons stimulating muscle contractions, generating heat through shivering.

Neonatal Thermoregulation

• Neonates may lack muscle mass, making shivering less effective. They utilize alternative methods to maintain warmth.

Regulation of Metabolism

• Thyroid Hormone Influence: Regulates metabolic rate impacted by growth, pregnancy, and lactation which, in turn, affects heat production.

• Metabolic Rate: 60-70% of heat is produced by just 10% of body mass.

Thermoneutral Zone

• Defined by upper and lower critical temperatures that influence an animal's body temperature relative to ambient conditions.

Case Study: Frizzle and Naked-Neck Hens

• Adaptations in Hot Climates: Higher egg mass and laying intensity observed in these breeds; suggests advantages in hot environments, though details of specific adaptations aren't essential.

Important Questions for Review

• Animal Health in Heat: Understand challenges pigs face in hot climates.

• Fever Mechanisms: Clarify what pyrogens are and their effect on body temperature.

• Anaesthetic Effects: Recognize how isoflurane may induce heat loss in animals.

• Skin Infections in Breeds: Discuss why breeds like the Shar Pei are susceptible to persistent skin infections.

Vitamin D Synthesis

• Essential Functions: Vitamin D plays a role as both a hormone and vitamin, crucial for calcium homeostasis.

• Two Forms: Vitamin D2 (dietary) and Vitamin D3 (synthesized in skin).

• Synthesis Process: Involves 7-dehydrocholesterol in the skin reacting to UV light; dense fur coats and heavy pigmentation can inhibit this synthesis.